Digital scan converter with programmable transfer function

Abstract

A digital scan converter is provided with a programmable transfer function for video display of picture elements (pixels) using a main random access memory for storing a pixel array to be read out periodically for display, and to be selectively read out while scanning for updating with a value derived from an auxiliary random access memory addressed by the composite of an old pixel value to be updated and the new pixel value. Each memory location of the auxiliary memory stores a value derived from a table defining the transfer function desired for the entire range of new and old pixel values. An alternate transfer function is stored in a second block of the memory and selectively called out by a prefix set to a 1 or 0 in the most significant bit position of the composite address word.

What is claimed is: 
     
       1. A method for processing video data in digital form, and storing it in an image memory for subsequent display, where the video data is developed by repeated scans and presented in the form of scan signals defining scan coordinates of picture elements, and a pixel value for each picture element, the steps of reading out of said image memory pixel values at locations corresponding to said scan coordinates,   providing an updated value for each new pixel value to be stored in said image memory from a set in an update memory as a function of (1) at least one old pixel value read out of said image memory at a location to be updated as defined by said scan coordinates, and (2) a new pixel value for the corresponding scan coordinates, said set having an appropriate updated value for every combination of an old pixel value and a new pixel value stored in an update memory location defined by a composite word including the combination of the old and new pixel values and at least one additional bit of greater significance,   selecting said at least one additional bit as a "1" or a "0" to provide for addressing one of said at least two parts of said update memory as a function of said old and new pixel values, each part having a different set of updated pixel values representing a selected transfer function,   receiving said old pixel value from said image memory and a new pixel value, forming said composite word with said at least one additional bit for addressing said update memory, and reading out an updated pixel value, and   storing said updated pixel value in said image memory at a location addressed by said scan coordinates corresponding to said new pixel value and previously used to address said image memory to read out said old pixel value.   
     
     
       2. The method of claim 1 including the step of reading out in parallel groups of adjacent pixel values stored in said image memory for display between processing cycles for incoming scans of video data, whereby video data is continually updated while it is displayed. 
     
     
       3. In a system for the processing of video data in digital form for subsequent display, where the video data is developed by repeated scans and presented in the form of scan signals defining scan coordinates of picture elements, and a pixel value for each picture element, the combination comprising an image memory for reading out pixel values at locations corresponding to said scan coordinates and storing in its place an updated pixel value,   a pixel value update memory for providing an updated pixel value to be stored in said image memory as a function of (1) at least one old pixel value read out of said image memory at a location to be updated as defined by said scan coordinates, and (2) a new pixel value for the corresponding scan coordinates, said update memory having at least two parts, each part having a different set of updated pixel values representing a transfer function, each part of said update memory having an appropriate updated value for every combination of an old pixel value and a new pixel value with the appropriate updated value stored in an update memory location defined by a composite word including the old and new pixel values and at least one additional bit of greater significance,   means for selectively setting said at least one additional bit to a "1" or a "0" to provide for addressing one of said at least two parts of said update memory as a function of said old and new pixel values,   means receiving said old pixel value for said image memory and said new pixel value for being combined with said at least one additional bit to form said composite word for addressing said update memory, thereby to read out an updated pixel value from said update memory, and   means for storing said updated pixel value in said image memory at a location addressed by said scan coordinates corresponding to said new pixel value and previously used to address said image memory to read out said old pixel value.   
     
     
       4. The combination of claim 3 including means for reading out in parallel groups of adjacent pixel values stored in said image memory for display between processing cycles for incoming scans of video data, whereby video data is continually updated while it is displayed. 
     
     
       5. In a system for processing video data in digital form, and storing said data in an image memory for subsequent display, where the video data is developed by repeated scans and presented in the form of scan signals defining scan coordinates of picture elements, and a new pixel value for each picture element, apparatus for updating data in said image memory with incoming video data according to predetermined transfer functions stored in an update memory, said update memory having at least two parts, each part having a different set of updated pixel values in accordance with a different transfer function, comprising means for reading out of said image memory pixel values at locations corresponding to said scan coordinates,   means for reading an updated value for each new pixel value to be stored in said image memory from said update memory,   means for receiving said old pixel value from said image memory and a new pixel value as a portion of composite address word, said address word including the combination of old and new pixel values and at least one additional bit of greater significance for addressing said update memory to read out an updated pixel value from said address,   means for setting said at least one additional bit to a "1" or a "0", and   means for storing said updated pixel value in said image memory at a location addressed by said scan coordinates corresponding to said new pixel value and previously used to address said image memory to read out said old pixel value.   
     
     
       6. Apparatus as defined in claim 5 including means for reading out in parallel groups of adjacent pixel values stored in said image memory for display between processing cycles for incoming scans of video data, whereby video data is continually updated in said image memory while it is continuously displayed.